A worldwide “critical shortage” of medical isotopes is expected due to the shutdown until late 2009 of a nuclear reactor in Ontario, Canada, according to Canadian authorities. The reactor, which stopped operations because of a heavy water leak, produces as much as 40% of the global supply of molybdenum 99 (99Mo), which decays to form technetium 99m (99mTc). 99mTc is currently used in approximately 80% of nuclear medicine scans.

According to Natural Resources Canada, the world's current supply of 99Mo is produced by 5 aging reactors in Belgium, Canada, France, the Netherlands, and South Africa. The shortage was expected to be exacerbated by the temporary closing of the Netherlands reactor for a month-long maintenance inspection from July 18 to August 18. Because the isotopes have a relatively short half life, they cannot be stockpiled.